1. Field of the Invention
The present invention relates generally to flat panel display technologies and, more particularly, to a flat panel display, such as a head mounted display and a process for its manufacture.
2. The Prior Art
Flat panel displays find many applications. Among these are computers, in particular lap-top computers, T.V. screens, video games and various military and space applications. Head mounted flat panel displays are smaller than conventional flat panel displays such as those employed in lap-top computers, T.V. screens and the like. Preferably, head mounted displays (HMDs) are of miniature size, i.e., about one inch square or less. For a representative HMD see U.S. Pat. No. 4,361,384 that issued to David A. Bosserman on Nov. 30, 1982, entitled "High Luminance Miniature Display." Miniature HMDs must not only be light in weight, they must also excel in luminance and must be rugged in construction. Adequate luminance is required in applications such as involving displays in aircraft cockpits or in submarine command centers. Adequate luminance also is required, in particular, where the miniature HMDs are in color.
Most present HMDs employ small cathode ray tubes (CRTs) for displaying visual information to an operator. As a consequence, they are heavy and cumbersome to handle. They also suffer from high power consumption and require large voltages to drive their CRTs. Improved versions of HMDs employ either photocathode image intensifiers, miniaturized CRTs or light emitting diodes (LEDs) for displaying visual information. See said U.S. Pat. No. 4,361,384. See also U.S. Pat. No. 5,060,027, that issued to Hart et al. on Oct. 22, 1991, entitled "Light Emitting Diode Array With Aligned Solder Bumps." Photocathode image intensifiers are, however, single purpose instruments since they cannot display information other than that emanating from the photocathode. Miniaturized CRTs and LED displays on the other hand, still suffer from excessive weights, high power consumption, limited resolution and safety problems.
Further improved versions of HMDs are hybrids in that they use thin film electroluminescent (TFEL) displays coupled to a photocathode image intensifier tube via a fiber optics input faceplate to provide a high luminance display adapted for use in daylight. See said U.S. Pat. No. 4,361,384; and also U.S. Pat. No. 4,733,128 that issued to Tohda et al. on Mar. 22, 1988; and U.S. Pat. No. 4,862,033 that issued to Migita et al. on Aug. 29, 1989. See also for an enhanced single-layer, multi-color luminescent display U.S. Pat. No. 4,987,339 that issued to James B. Robertson on Jan. 22, 1991. The addition of the photocathode image intensifier tube adds however to the cost, the weight and to the complexity of the resultant high luminance display system. It also eliminates the possibility of having such a system operated in full color. HMDs based on reflection systems on the other hand, in which an image is formed by an LED array and projected to an observer via an optical path, lack the resolution necessary for providing a high quality visual information. See said U.S. Pat. No. 5,060,027 in conjuction with said U.S. Pat. No. 4,361,384.
In addition to the requirement for adequate brightness of the display, even during brilliant daylight prevailing in aircraft cockpits, HMDs must meet demanding packaging and interconnect requirements. For, the smaller is the HMD, the more demanding become its packaging and interconnect requirements. In the manufacture of microelectronic devices, which require a large number of electrical connections, a new technology appropriately named flip-chip bump-bond technology, was developed to provide such a high yield interconnect despite packaging density. "Flip chip bonding lends itself to high packaging densities, faster circuits, and eliminates wire bonding. Various methods to obtain reliable processes are being investigated by many corporations. In general, a metal bump is grown on the chip, the substrate, or both. The chip is flipped over, aligned to the substrate, and bonded." See Michael Schneider, "Flip Chip Bonding Offers Packaging Alternative," Hybrid Circuit Technology, March 1988, pp. 29-31. Such flip-chip technology was applied, amongst others, to the manufacture of large scale integrated (LSI) silicon circuits on glass substrates, and to the manufacture of ferroelectric components. See U.S. Pat. No. 4,190,855 that issued to Yukihiro Inoue on Feb. 26, 1980 and U.S. Pat. No. 5,070,026 that issued to Anton C. Greenwald et al. on Dec. 3, 1991, respectively. The latter U.S. Pat. No. 5,070,026 is assigned to a common assignee herein, to wit, Spire Corporation, Bedford, Mass. The flip-chip technology may have shown the way, yet its application to the manufacture of HMDs was still troublesome. As evident from said U.S. Pat. No. 5,060,027 to Hart et al, in the manufacture of LED arrays by flip-chip technology, the numbers and positions of the solder bumps must correspond to the numbers and positions of the LEDs, with "each driver circuit having a corresponding contact" with an LED. This requirement as to numbers and positions of drivers and corresponding contacts has thus far limited the practicality and use of miniature HMDs, in particular HMDs intended for full color use.